A system is known by the German patent application Ser. No. 3 042 946 in which one of the supply rollers is moved away from the other supply roller simply by a core electrical device controlled by a yarn detector, the first roller moving only according a rectilinear path to disengage or engage the second roller.
A system is also known from German Patent of Addition No. 515.088 in which the yarn break automatically causes the tilting of a lever which, in turn, controls a complex counterweight rodding system.
From Belgian Patent No. 769.257 is also known a system in which a yarn break causes the tilting of a thread-guide which, in turn, via an excentric, causes the longitudinal sliding of a double arm carrying one of the supply rollers of two pairs of rollers in order to retract it from the other roller of each pair.
These various known systems are fragile, complex and costly.